Scatterometry metrology using inelastic scattering

ABSTRACT

A system for characterizing material properties in miniature semiconductor structures performs a scatterometry analysis on inelastically scattered light. The system can include a narrowband probe beam generator and a detector. A single wavelength probe beam from the narrowband probe beam generator produces scattered light from a measurement pattern on a test sample. The scattered light is measured by the detector, and the measurement data (e.g., Raman spectrum) is used in a scatterometry analysis to determine material properties for the measurement pattern. The detector can measure either incoherent inelastically scattered light (e.g., using a spectrometer) or coherent inelastically scattered light (e.g., using an array detector). If the measurement pattern dimensions are substantially similar to actual device dimensions, the material property distributions determined for the measurement pattern can be applied to the actual devices on the test sample.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/182,171, entitled “Scatterometry Metrology Using InelasticScattering” filed Jul. 15, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of metrology, and in particular, to asystem and method for accurately and efficiently measuring semiconductorstructure characteristics.

2. Related Art

Integrated circuit (IC) device geometries continue to shrink with eachgeneration of process technology. Those size reductions providesignificant efficiency and performance benefits in modern ICs. At thesame time, the production of such ICs requires increasinglysophisticated and precise manufacturing processes, which in turnrequires that highly sensitive metrology techniques and tools be used toensure proper manufacturing results. Currently, one of the mosteffective metrology techniques for modern ICs is scatterometry, in whichlight scattered from a pattern on a wafer is used to determine physicalcharacteristics for structures formed on that wafer. The two mainmethods of performing scatterometry are spectroscopic scatterometry andsingle wavelength scatterometry.

FIG. 1A shows a spectroscopic scatterometry system 100A for performingmetrology on a test sample 190A. Spectroscopic scatterometry system 100Aincludes a broadband light source 110A, focusing optics 120A, a stage130A for supporting test sample 190A, an order blocking aperture 135A,analyzing optics 140A, a spectrometer 145A, and an array detector 150A.To perform a scatterometry measurement, light source 110A generates abroadband probe beam 111A (i.e., a light beam that includes a wide rangeof wavelengths, such as a white light), which focusing optics 120Adirects onto a measurement pattern 191A on test sample 190A. Note thatin some spectroscopic scatterometry systems, focusing optics 120A (andanalyzing optics 140A) can include polarizing elements to enableellipsometric analyses to be performed on the scattered light. Notefurther that, unlike most optical metrology tools, scatterometry toolssuch as system 100A generally require a physical pattern on the testsample being measured, so that sufficient light scattering (which isgenerally due to diffraction effects in the test pattern) occurs.

The scattered light 112A created by diffraction at test sample 190A iscomposed of a plurality of output beam components called orders, eachwith its own direction of propagation. Each of the diffraction ordershas its own polar angle (angle with respect to wafer normal) and its ownazimuthal angle (angle with respect to the projection of the probe beam111A in the plane of the wafer). There is usually a component emittedwith a polar angle equal to the polar angle (angle of incidence) of theprobe beam 111A and with an azimuthal angle relative to probe beam 111Aof 180 degrees. This component (identified in FIG. 1A as zeroth orderbeam 112A(0)) is defined as the zeroth diffraction order and correspondsto the reflected beam from an unpatterned sample. The presence ofmeasurement pattern 191A creates other diffraction orders (e.g.,negative first order beam 112A(−1) and first order beam 112A(+1)) withother polar angles, both greater than and smaller than the zeroth polarangle. If pattern 191A is one-dimensional and if the projection of theprobe beam 111A onto the wafer is aligned with a symmetry axis ofpattern 191A, all diffraction orders will have an azimuthal angle of 180degrees relative to probe beam 111A. Otherwise, orders with otherazimuthal angles may also be present. This asymmetric situation iscalled conical diffraction. In general, the polar (and in some casesazimuthal) angles for all diffraction orders other than the zeroth orderdepend on wavelength. Therefore all diffraction orders other than thezeroth order are not narrow beams, but instead include a variety ofcomponents having various polar and azimuthal angles.

A portion of the scattered light 112A generated in response to broadbandlight beam 111A is collected by analyzing optics 140A. Often only thezeroth order light is collected (e.g., beam 112A(0), but other ordersmay also be collected. Zeroth order beam 112A(0) is selected by orderblocking aperture 135A, and then passes through analyzing optics 140A,after which it is dispersed by spectrometer 145A onto array detector150A. Array detector 150A measures a broadband spectrum of intensitiesfor the various wavelengths of light making up broadband light beam111A. This output spectrum provides a “pattern signature” that isrepresentative of the particular dimensional characteristics ofmeasurement pattern 191A (e.g., dimensions, composition, and surfaceroughness). By analyzing the broadband spectrum (or spectra) measured byarray detector 150A in conjunction with mathematical modeling ofmeasurement pattern 191A, the desired physical characteristicinformation of measurement pattern 191A can be determined, even if thosephysical dimensions are smaller than the wavelengths of light inbroadband light beam 111A.

FIG. 1B shows a single wavelength scatterometry system 100B forperforming metrology on a test sample 190B. Spectroscopic scatterometrysystem 100B includes a narrowband light source 110B, focusing optics120B, a stage 130B for supporting test sample 190B, analyzing optics140B, and an array detector 150B. To perform a scatterometrymeasurement, light source 110B generates a narrowband light beam 111B(i.e., a light beam that includes a single wavelength, such as a laserlight), which focusing optics 120B directs onto a measurement pattern191B on test sample 190B. As described with respect to scatterometrysystem 100A shown in FIG. 1A, focusing optics 120B (and analyzing optics140B) can include polarizing elements to enable ellipsometric analysesto be performed on the scattered light 112B that is scattered frommeasurement pattern 191B in response to light beam 111B.

The scattered light 112B is directed by analyzing optics 140B onto arraydetector 150B, which measures the intensity and directions of the lightscattering from measurement pattern 191B. In this case the variousdiffraction orders making up scattered light 112B (e.g., first orderbeam 112B(+1), zeroth order beam 112B(0), and negative first order beam112B(−1)) are all narrowband beams and each has a unique polar andazimuthal angle because there is only a narrow range of wavelengthspresent in narrowband probe beam 111B. Array sensor 150B measures theintensity and positions of some fraction of the diffraction orders.Knowing the position on the array sensor, combined with the propertiesof analyzing optics 140B, it is possible to extract the polar andazimuthal angle of each detected diffraction order. The arrangement ofdiffraction orders, their individual intensities, their polarizationproperties, and their polar and azimuthal angles depend on theproperties of pattern 191B and therefore constitute a “patternsignature” for pattern 191B. This pattern signature can be used withmathematical modeling to extract dimensional and other parameters ofpattern 191B.

It is possible to extract even more information about the measurementpattern with either the spectroscopic or narrow band systems bymeasuring with probe beams of different angles. The angles and spectraof the various diffraction orders depend on both the polar angle andazimuthal angle of the probe beam. For instance, it is possible tomeasure at different probe azimuthal angles by rotating the wafer in itsown plane by means of a rotational mechanism incorporated into stage190A (shown in FIG. 1A) or 190B (shown in FIG. 1B). Measurements can betaken at two or more angles in sequence, rotating the wafer to thedesired azimuthal angle before each measurement. In this case the restof the measurement system can remain stationary. Measurements can alsobe made at multiple polar angles, but this requires moving at least oneor more of the modules of the measurement system.

In all these scatterometry systems, the scattered light has the samewavelength as the probe light. In the spectroscopic systems eachwavelength component of the scattered light is created by exactly thesame wavelength component of the probe light. In the narrow-band systemall of the scattered light is in the same narrow wavelength range of theprobe light. The equality of scattered and probe wavelengths is calledelastic scattering, due to the fact that the scattered photons have thesame energy as the probe photons and no energy is gained or lost to thesample.

Thus, scatterometry (both spectroscopic scatterometry and singlewavelength scatterometry) provides metrology capabilities that typicallyexceed the capabilities of most other non-destructive measurementtechniques, and accordingly is the technique of choice for measuring theextremely small semiconductor structures in advanced ICs. However, asscaling of semiconductor devices extends further into the sub-micronrange, material properties (i.e., material characteristics other thandimension) such as stress, strain, embedded charge, composition, anddegree of crystallinity become increasingly important.

For example, material stress plays a significant role in the performanceof the miniature transistors used in advanced ICs. Because materialstress is affected by structure size, the stress within, for example,the active region of a MOS transistor cannot be determined from a stressmeasurement on a bulk region of a wafer. Unfortunately, conventionalstress measurement techniques are mainly directed toward bulkmeasurements (e.g., the measurement of stress within a film formed overan entire wafer), and are therefore not effective for device-levelmeasurements. For example, Raman spectroscopy is one conventional stressmeasurement technique for measuring stress in silicon (Si) and silicongermanium (SiGe) structures on semiconductor wafers. Raman scatteredlight usually is composed of several discrete narrow wavelength outputbeam components, shifted both above and below the incident narrowwavelength range. The magnitude of the wavelength shift of the highestintensity shifted component is determined by the stress level in thesilicon. In a silicon germanium structure the shift of this highestintensity shifted component is determined by both the stress within thesilicon germanium and the particular silicon germanium composition(other output beam components exhibit intensities and wavelength shiftsthat are mainly affected by silicon germanium composition). Therefore,the measured shifts and intensities of the various output beamcomponents can be used to determine the stress and composition of Si andSiGe. A similar process can be used to measure other crystalline andpolycrystalline materials. Raman spectroscopy has been combined withhigh resolution microscopy to make measurements with a spatialresolution down to about 0.5 um. However, this level of spatialresolution is not sufficient for making measurements on advancedsemiconductor structures that have dimensions of less than 500 nm.

Accordingly, it is desirable to provide a method and system formeasuring material properties in miniature devices and structures.

SUMMARY OF THE INVENTION

The characterization of material properties in modern advanced ICs isbecoming increasingly important due to the significant effects suchmaterial properties have on device performance. Unfortunately,conventional metrology techniques are typically limited to measurementson structures having dimensions much greater than the wavelength oflight used in a probe beam, and are therefore not well suited to measurematerial properties in actual device structures. To overcome thislimitation of conventional metrology techniques, a metrology method andsystem can measure light scattered inelastically (i.e., light scatteredwith a different wavelength than the incident light) from a measurementpattern. By applying scatterometry techniques in analyzing theinelastically scattered light, material property data can be determinedfor the structures making up the measurement pattern, even if thepattern structure dimensions are smaller than the wavelength of theprobe beam. In addition, by sizing the pattern structures to bedimensionally similar to actual device structures, the material propertydata determined for the pattern structures can be applicable to theactual device structures.

In one embodiment, a metrology system can include a beam generator fordirecting a narrowband probe beam (e.g. a laser or a broadband lightsource limited to a single wavelength by a monochromator) at ameasurement pattern on a test sample and a sensor for measuringinelastic scattering data (e.g., Raman spectra) for light scattered fromthe measurement pattern in response to the narrowband probe beam.Scatterometry analysis logic (either external to or incorporated intothe metrology system) can then process the inelastic scattering datameasured by the sensor to determine material property distribution(s)within the measurement pattern.

In various embodiments, the metrology system can include input opticsfor directing the narrowband probe beam at the measurement pattern, ablocking filter for filtering scattered light having the same wavelengthas the narrowband probe beam, output optics for directing theinelastically scattered light onto the sensor (which can include aspectrometer and/or array detector, among other types of sensors),and/or adjustment mechanism(s) for changing the polar and/or azimuthalangle between the narrowband probe beam and the test sample pattern. Inanother embodiment, the beam generator can include capabilities foradjusting the wavelength of the narrowband probe beam and the blockingfilter in the analyzing optics. In another embodiment, the metrologysystem can include additional means for performing standardscatterometry to determine dimensional characteristics of themeasurement pattern that can be used in the analysis of the inelasticscattering data.

In another embodiment, a method for analyzing a test sample can includegenerating inelastic scattered light from a measurement pattern on thetest sample, measuring the inelastically scattered light, and analyzingthe measured data (e.g., Raman spectrum) to determine a materialproperty distribution in the measurement pattern. In one embodiment,multiple sets of inelastic scattering data can be generated by varyingthe polar angle, the azimuthal angle, and/or the wavelength of thenarrowband probe beam used to generate the (either incoherent orcoherent) inelastically scattered light. In one embodiment, the analysisof the inelastic scattering data can involve generating trial (expected)inelastic scattering data based on a trial distribution(s) for thematerial property (properties) and a mathematical model for themeasurement pattern, comparing the trial inelastic scattering data tothe measured inelastic scattering data, and adjusting the trialdistribution(s) until the trial inelastic scattering data matches themeasured inelastic scattering data. In another embodiment, a standardscatterometry operation can be performed on the measurement pattern todetermine physical characteristics (i.e., dimensional characteristics)of the measurement pattern that can be used in the generation of themathematical model.

The invention will be more fully understood in view of the followingdescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams of conventional scatterometry systems.

FIGS. 2A and 2B are diagrams of a metrology system based on incoherentinelastic scattering from a measurement pattern.

FIG. 2C is a diagram of a metrology system based on coherent inelasticscattering from a measurement pattern.

FIGS. 3A and 3B are flow diagrams of a method for performingscatterometry based on inelastically scattered light.

DETAILED DESCRIPTION

The characterization of material properties in modern advanced ICs isbecoming increasingly important due to the significant effects suchmaterial properties have on device performance. Unfortunately,conventional metrology techniques are typically limited to measurementson structures having dimensions much greater than the wavelength oflight used in a probe beam, and are therefore not well suited to measurematerial properties in actual device structures. To overcome thislimitation of conventional metrology techniques, a metrology method andsystem can measure light scattered inelastically (i.e., light scatteredwith a different wavelength than the incident light) from a measurementpattern. By applying scatterometry techniques in analyzing theinelastically scattered light, material property data can be determinedfor the structures making up the measurement pattern, even if thepattern structure dimensions are smaller than the wavelength of theprobe beam. In addition, by sizing the pattern structures to bedimensionally similar to actual device structures, the material propertydata determined for the pattern structures can be applicable to theactual device structures.

As noted above, Raman spectroscopy is sometimes used to measure stressin silicon or silicon germanium device structures. Raman scattered lightis a type of inelastically scattered light that is incoherent and has nofixed phase relation to the probe light. Incoherent inelasticallyscattered light exhibits no diffraction and no discrete scattered beamsor orders. Therefore, Raman scattered light is diffuse and is emitted inall directions with a smooth variation in intensity versus direction.The scattering is generally weak and it is preferable to use a high N.A.objective in the analyzing optics to collect as much scattered light aspossible.

FIG. 2A shows a metrology system 200A that incorporates incoherentinelastic scattering analysis capabilities in accordance with anembodiment of the invention. Metrology system 200A includes a beamgenerator 210A, focusing optics 220A, a stage 230A for supporting a testsample 290A, a blocking filter 241A, analyzing optics 242A, spectrometeroptics 243A, a spectrometer 250A, and an array detector 252A. Acomputing system 260A (described in greater detail below) can be coupledto (e.g., via a data cable or network) or incorporated into metrologysystem 200A to perform analysis on the data gathered by array detector252A. In various embodiments, metrology system 200A can also includemultiple sensors and/or optics to provide additional metrologycapabilities, as indicated by optional optics 255A and sensor 256A.Sensor 256A can represent any type and number of detection elements,such as additional spectrometer/detector combinations, intensitydetectors, and/or array detectors, among others. For example, in oneembodiment, sensor 256A could be an array detector, thereby providingmetrology system 200 with standard scatterometry capabilities (e.g., asdescribed with respect to FIGS. 1A and/or 1B).

To perform a scatterometry operation, beam generator 210A generates aprobe beam 211A that is directed onto a measurement pattern 291A on testsample 290A by focusing optics 220A. Ideally, the structures withinmeasurement pattern 291A will be dimensionally similar to actual devicesin test sample 290A (i.e., same size structures with the same orpossibly larger spacing), thereby allowing the measurement resultsgenerated by metrology system 200A to be applicable to the actualdevices in test sample 290A. Probe beam 211A is a narrowband beam oflight, i.e., a beam of light having a single wavelength. In oneembodiment, beam generator 210A could supply probe beam 211A as abroadband beam (i.e., multi-wavelength beam), and focusing optics 220Acould include a monochromator to ensure that only a single wavelength oflight reaches test sample 290A. In another embodiment, beam generator210A could produce probe beam 211A as a narrowband beam (e.g., beamgenerator 210A can comprise a laser) at a desired wavelength. In oneembodiment, beam generator 210A can include wavelength adjustmentcapabilities to allow probe beams 211A with different wavelengths to bedirected at test sample 290A during different measurement operations. Inanother embodiment, metrology system 200A could include multiple beamgenerators, as indicated by optional beam generator 215A, for directingdifferent probe beams at test sample 290A during sequential orconcurrent measurement operations.

In any case, in response to narrowband probe beam 211A, scattered light212A is scattered from measurement pattern 291A. The scattered light iscollected by analyzing optics 242A. As is known in the art, most of thescattering from measurement pattern 291A will result from elastic (orRayleigh) scattering, so that most of the light rays in scattered light212A will have the same wavelength as probe beam 211A. Conventionalscatterometry systems (e.g., scatterometry systems 100A and 100B inFIGS. 1A and 1B, respectively) measure and analyze elastically scatteredlight to determine dimensional information for the measurement pattern.

However, a small portion of scattered light 212A will be due toinelastic scattering, resulting in light rays having wavelengthsdifferent than the wavelength of probe beam 211A (e.g., rays 212A(1) and212A(2)). To prevent the stronger signal from elastically scatteredlight from overwhelming the measurement of the inelastically scatteredlight, blocking filter 241A filters out the elastically scatteredportions of scattered light 212A while passing the inelasticallyscattered light 213A (e.g., rays 212A(1) and 212A(2)). The inelasticallyscattered light is then directed by spectrometer optics 243A ontospectrometer 250A, which disperses the light onto array detector 252A.The spectrum of inelastically scattered light measured by array detector252A provides a pattern signature for measurement pattern 291A.

Unlike the spectrum of elastically scattered light measured in aconventional scatterometry system (e.g., scatterometry system 100A), thespectrum of inelastically scattered light (e.g., the “Raman spectrum”)includes material property information beyond the basic physicalcharacteristics of measurement pattern 291A. This additional materialproperty information is available due to the fact that inelasticscattering occurs when vibrational energy (phonons) from the scatteringstructures (e.g., measurement pattern 291A) are added to or subtractedfrom the incident light (e.g., narrowband probe beam 211A). Thenarrowband probe beam 211A creates a complex array of optical electricfields in measurement pattern 291A, and those optical electric fieldsadd or subtract phonons of specific energies to create inelasticallyscattered light 212A. The particular phonon energies added to and/orsubtracted from the incident light in narrowband probe beam 211A arestrongly related to the material properties of the scattering structure(i.e., measurement pattern 291A). For example, the location of one ofthe peaks in the Raman spectrum is sensitive to the amount of strain inthe scattering structure. Therefore, by analyzing the corresponding peakwithin a Raman spectrum measured by spectrometer 250A, the amount ofstrain in measurement pattern 291A can be determined.

Note that as the polar angle (i.e., the complement of angle of incidenceθ) and/or the azimuthal angle φ between probe beam 211A and measurementpattern 291A change, the distribution of optical electric fieldsgenerated in measurement pattern 291A changes, thereby resulting inRaman spectra that emphasize different material properties at differentlocations within measurement pattern 291A. Therefore, in one embodiment,by measuring Raman spectra at multiple polar and/or azimuthal angles,the material properties at various locations within measurement pattern291A can be determined. In this manner, the material propertydistributions (e.g., the strain distribution) within measurement pattern291A can be measured at subwavelength spatial resolutions, just asstandard scatterometry systems can measure subwavelength dimensions. Inanother embodiment, similar spatial resolution can be achieved bymeasuring Raman spectra over a range of wavelengths for probe beam 211A(in which case beam generator 210A could be an adjustable wavelengthbeam generator).

For example, in one embodiment, metrology system 200A can be configuredto measure strain in silicon formed over silicon germanium. Becausesilicon has a smaller lattice size than silicon germanium, a siliconlayer formed on top of a silicon germanium layer will exhibitsignificant induced strain. This strain can actually enhance deviceperformance by improving carrier mobility. Historically, strain has beenmeasured using the micro-Raman techniques, in which the Raman spectrumof a test film is analyzed to determine strain. However, because strainis highly dependent on structure size (e.g., 25 nm and below foradvanced semiconductor devices), a strain measurement performed on abulk film (i.e., a larger film such as a blanket film over an entirewafer) will not match the strain present in an actual device.Unfortunately, because the measurement spot of the highest resolutionmicro-Raman tools is on the order of 0.5 μm, conventional strainmeasurement techniques cannot effectively measure strain in modern ICstructures.

However, the use of pattern-based Raman spectrum generation, asdescribed above with respect to FIG. 2A, overcomes these limitations ofconventional techniques, and enables accurate strain measurements oneven the smallest semiconductor structures. For example, beam generator210A could be an argon ion laser generating a probe beam 211A with awavelength of 488 nm, and focusing optics 220A could focus probe beam211A down to a 50 um×50 um spot on measurement pattern 291A

In one embodiment, metrology system 200A can include an optionalpositioning mechanism 216A to allow angle of incidence θ to be scannedbetween a selected range (e.g., 0° to 70°) while maintaining the spotilluminated by probe beam 211A at the same location on measurementpattern 291A. Note that the specific position and configuration ofpositioning mechanism 216A is exemplary only, and alternative and/oradditional positioning mechanisms (such as steppers, x-y tables,gimbals, goniometers, and any other mechanisms) can be included anywherewithin metrology system 200A. For example, stage 230A can include arotational positioning mechanism 231A for changing the azimuthal angle φof probe beam 211A relative to measurement pattern 290A. In anotherembodiment, analyzing optics 240A can include a collection lens forfocusing the (filtered) inelastically scattered light 217A ontospectrometer 250A, with the collection lens having a large enoughnumerical aperture to collect the scattered light from the entire rangeof angles of incidence θ without moving. The resulting inelasticallyscattered light data (e.g., Raman spectra) measured by spectrometer 250Acould then be used to generate a strain map across measurement pattern291A, thereby allowing the strain exhibited by individual structureswithin measurement pattern 291A to be accurately determined.

In another embodiment, focusing optics 220A can include a polarizer andanalyzing optics 242A can include an analyzer to allow polarizationanalysis to be performed on the incoherent inelastically scattered light217A. Specifically, the polarizer could apply a specific polarization tonarrowband probe beam 211A, and the analyzer could enable the change inpolarization state exhibited by scattered light 217A.

The actual analysis of the inelastically scattered light data measuredby metrology system 200A is performed by computing system 260A.Computing system 260 includes inelastic scatterometry logic 261A foranalyzing the measurement data produced by detector 252A. In oneembodiment, computing system 260A can also include optional standardscatterometry logic 262A for performing standard scatterometry analyses(e.g., as described with respect to FIG. 1B). Computing system 260A canbe any type of system for performing automated data analysis, such as apersonal computer or a thin client running off of a network server.Likewise, Inelastic scatterometry logic 261A can be any control logic(e.g., software or hardware logic) for causing computing system 260A toperform the appropriate analysis of the Raman spectra measured bydetector 252A.

For example, in one embodiment, inelastic scatterometry logic 261A canperform an iterative operation to determine the material propertydistribution(s) across measurement pattern 291A. A trial materialproperty distribution is estimated for measurement pattern 291A, and theexpected Raman spectra (or any other measurement data for inelasticallyscattered light 212A) for each angle of incidence (90-θ) and/orazimuthal angle φ and/or wavelength for narrowband probe beam 211A iscalculated from a mathematical model of measurement pattern 291A. Theactual measured Raman spectra (from spectrometer 250A) are then comparedto the expected Raman spectra. Based on the differences between theexpected and measured Raman spectra, the trial material propertydistribution is adjusted to generate a new set of expected Raman spectrato be compared to the measured Raman spectra. This process continuesuntil a desired match is detected between the expected and measuredRaman spectra, at which point the trial material property distributioncan be provided as the final material property distribution (i.e., themeasurement result of the scatterometry process).

FIG. 2B shows another embodiment of a metrology system 200B thatincorporates capabilities for analyzing incoherent inelastic scatteringfrom a sample pattern. Metrology system 200B is substantially similar to(and operates in a manner substantially similar to) metrology system200A shown in FIG. 2A, except that probe beam directional control isprovided by a beamsplitter 244B. In addition to beamsplitter 244B,Metrology system 200B also includes a narrowband beam generator 210B,focusing optics 220B, a stage 230B for supporting a test sample 290B, ablocking filter 241B, analyzing optics 242B, spectrometer optics 243B, aspectrometer 250B, and an array detector 252B. A computing system 260Bcan be coupled to or incorporated into metrology system 200B to performanalysis on the data gathered by spectrometer 250B. In variousembodiments, metrology system 200B can also include multiple sensors toprovide additional metrology capabilities, as indicated by optionalsensor 255B. Sensor 255B can represent any type and number of detectionelements (and associated optics), such as an additional spectrometer, anintensity detector, or an array detector, among others. For example, inone embodiment, sensor 255B could be an array detector, therebyproviding metrology system 200B with standard scatterometry capabilities(e.g., as described with respect to FIGS. 1A and/or 1B).

To perform a measurement operation, beam generator 210B generates anarrowband probe beam 211B that is directed onto a measurement pattern291B on test sample 290B by means of beamsplitter 244B and analyzingoptics 242B. The incoherent inelastically scattered light 212B generatedin response to probe beam 211B is collected by analyzing optics 242B,passes through beamsplitter 244B, and is filtered by blocking filter241B. The elastically scattered light rays do not pass through blockingfilter 241B, while the incoherent inelastically scattered light rays212B(1) and 212B(2) pass through blocking filter 241B and are focusedonto spectrometer 250B by spectrometer optics 243B. The polar angle(i.e., the complement of angle of incidence 8) of probe beam 211B can beadjusted by moving beam generator 210B and focusing optics 220Bvertically (for example using optional positioning mechanism 2168),while the azimuthal angle of measurement pattern 291B can be adjustedusing optional rotational positioning mechanism 231B in stage 2303.Furthermore, just as described with respect to FIG. 2A, beam generator210B can include the capability to generate narrowband probe beam 211Bover a range of wavelengths.

Once a set of inelastically scattered light data (e.g., Raman spectra)has been measured by detector 252B for a variety of polar and/orazimuthal angles and/or probe beam wavelengths, inelastic scatterometrylogic 261B (e.g., software or hardware logic) in computing system 260B(e.g., a personal computer, server, or embedded computing resources) cananalyze that data in substantially the same manner as described withrespect to computing system 260A in FIG. 2A to generate materialproperty data for measurement pattern 291B.

Note that in one embodiment, computing system 260B can also includeoptional standard scatterometry logic 262B for performing standardscatterometry analyses on data gathered by optional detector 255B. Forexample, elastically diffracted light 260B, which is generated inresponse to probe beam 211B at the same time that inelasticallyscattered light 212B is generated and which includes of one or morediffracted orders, can be directed by analyzing optics 242B andbeamsplitter 244B onto optional detector 255B. Detector 255B may consistof any number of optical elements and detectors necessary to perform anelastic scatterometry analysis on diffracted light 260B (as describedwith respect to FIG. 1B). Optional detector 255B may also be movedvertically or may have a large enough aperture to collect elastic lightat a range of polar angles without adjustment.

Note further that any type of incoherent inelastic scatteringprocess(es) can be used by metrology systems 200A and 2008 to generateinelastically scattered light 212A and 212B, respectively, for themeasurement of material properties. Some of these processes arephotoluminescence, fluorescence, phosphorescence, Brillouin scattering,as well as others. For example, photoluminescence involves the use of anarrowband probe beam to create electron-hole pairs in silicon orsilicon germanium. The electron-hole pairs recombine and createincoherent light with a range of wavelengths longer than the probe beam.The photoluminescence spectrum can then be used as a measure of crystaldislocations and defects in the silicon or silicon germanium.

Note further that in addition to incoherent inelastic scatteringprocesses, coherent inelastic scattering processes also exist that maybe used to generate the inelastically scattered light for use in ascatterometry analysis to determine material properties. For example,one such process is second harmonic generation, which occurs when anintense narrowband probe beam is incident upon the surface of a materialand generates an output beam with a wavelength exactly half the probewavelength. It is preferable for the source of the probe beam to be apulsed laser with a large peak power for best efficiency of secondharmonic generation. In the past, second harmonic generation has beenused to determine electric fields and trapped charge at the surface ofrelatively large silicon and silicon germanium structures.

FIG. 2C is an embodiment of a metrology system 200C for generatingmaterial property measurements based on coherent inelastic scatteringfrom sample patterns. Metrology system 200C includes a beam generator210C, focusing optics 220C, a stage 230C for supporting a test sample290C, analyzing optics 242C, a blocking filter 241C, an array detector252C, and a computing system 260C. To perform a measurement operation,beam generator 210C generates an intense narrowband probe beam 211C thatis directed onto a measurement pattern 291C on test sample 290C byfocusing optics 220C. The coherent inelastically scattered light 212C iscollected by analyzing optics 242C, and is then passed through blockingfilter 241C to filter out any elastically scattered light. The coherentinelastically scattered light passes through the filter and is detectedby detector 252C.

In one embodiment, detector 252C can be an array detector to measure thespatial distribution of multiple diffracted orders (e.g., as indicatedby negative first order beam 212C(−1), zeroth order beam 212C(0), andfirst order beam 212C(+1)), or may be a single intensity detector for asingle order. The measurements may be taken at multiple wavelengths byadjusting the wavelength of the beam generator 210C (or by usingadditional optional beam generators 215C), and/or may be taken atmultiple polar angles by adjusting the position of source 210C relativeto stage 230C (e.g., via optional positioning mechanism 216C), and/ormay be taken at multiple azimuthal angles by rotating test sample 290Cin its own plane (e.g., via optional rotational mechanism 231C in stage230C).

Once a number of measurements have been taken for a range of polarand/or azimuthal angles and/or probe beam wavelengths, inelasticscatterometry logic 261C (e.g., software or hardware logic) in computingsystem 260C (e.g., a personal computer, server, or embedded computingresources) can analyze those spectra in substantially the same manner asdescribed with respect to computing system 260A in FIG. 2A to generatematerial property data for measurement pattern 291C. Note that likecomputing system 260A, computing system 260C can include optionalstandard scatterometry logic 262C for performing standard scatterometryanalyses.

Note further that coherent inelastically scattered light 212C caninclude diffraction orders not present in incoherent inelasticallyscattered light. Therefore, in addition to logic substantially similarto that present in inelastic scatterometry logic 261A, inelasticscatterometry logic 261C can also include logic for analyzing theangular and intensity arrangement of those diffraction orders incoherent inelastically scattered light 212C to extract additionalinformation about measurement pattern 291C.

Note further that any type of coherent inelastic scattering process(es)can be used by metrology system 200C to generate inelastically scatteredlight 212C. For example, other techniques for generating coherentinelastically scattered light include third harmonic generation, opticalmixing, 4-wave mixing, CARS (coherent anti-Stokes Raman scattering), andstimulated Raman scattering, among others.

FIG. 3A shows a flow diagram of the metrology operation described withrespect to FIGS. 2A, 2B, and 2C. First, in an optional “STANDARDSCATTEROMETRY” step 305, a standard scatterometry operation can beperformed (e.g., as described with respect to FIGS. 1A and 1B) todetermine physical dimensions of the measurement pattern (291A, 291B,and 291C in FIGS. 2A, 2B, and 2C, respectively) on the test sample(290A, 290B, and 290C in FIGS. 2A, 2B, and 2C, respectively). Thisphysical dimension data can then be used during subsequent dataanalysis, as described in greater detail below. Note that while step 305is depicted at the start of the flow diagram for exemplary purposes, invarious other embodiments, step 305 can be performed at any point priorto the final data analysis (i.e., step 360).

In a “NARROWBAND BEAM GENERATION” step 310, a narrowband probe beam(e.g., probe beams 211A, 211B, and 211C in FIGS. 2A, 2B, and 2C,respectively) is generated. Then, in a “PATTERN FOCUSING” step 320, thenarrowband probe beam is directed onto the measurement pattern in thetest sample. The resulting inelastically scattered light (e.g.,inelastically scattered light 212A, 212B, and 212C in FIGS. 2A, 2B, and2C, respectively) is then directed onto a sensor (e.g., spectrometer250A and detector 252A in FIG. 2A, spectrometer 250B and detector 252Bin FIG. 2B, and array detector 252C in FIG. 2C) and measured in an“INELASTIC SCATTERING DETECTION” step 330. If measurements are to betaken at additional polar and/or azimuthal angles for the probe beam, an“ADDITIONAL ANGLES?” step 340 can loop the process back to step 310.Similarly, if measurements are to be taken using probe beams havingdifferent wavelengths, an “ADDITIONAL WAVELENGTHS?” step 350 can alsoloop the process back to step 310. Once all the various measurementconditions have been satisfied, the measured inelastically scatteredlight data (e.g., Raman spectra) can be analyzed in a “DATA ANALYSIS”step 360 to determine a material property distribution(s) for themeasurement pattern (e.g., stress distribution, dopant concentrationdistribution, crystallinity distribution, charge distribution).

FIG. 3B shows a flow diagram of an embodiment of a data analysis processfor the measured inelastically scattered light data gathered in steps310-350. In a “CREATE PATTERN MATHEMATICAL MODEL” step 361, amathematical model is generated for the optical behavior of themeasurement pattern. Note that the mathematical model can incorporatethe dimensional data generated by standard scatterometry in optionalstep 305 (described above with respect to FIG. 3A). Then, in a “GENERATETRIAL MATERIAL PROPERTY DISTRIBUTION(S)” step 362, a trial set ofmaterial property data is specified for the measurement pattern. Themathematical model is then used to generate a set of expectedinelastically scattered light data (e.g., Raman spectra) using the trialmaterial property distribution(s) in a “GENERATE TRIAL INELASTICSCATTERING DATA” step 363. The expected data is compared to the measureddata, and if a match (to a desired tolerance) is not detected in a“MATCH?” step 365, the process loops back to step 362, where the trialmaterial property distribution is modified, and a new set of trial datais generated in step 363 for comparison against the measured data instep 364. The process continues to loop in this manner until a matchbetween the measured and expected data is detected in step 365, at whichpoint the trial material property distribution(s) can be presented asthe measurement output in a “MEASUREMENT OUTPUT” step 366.

The various embodiments of the structures and methods of this inventionthat are described above are illustrative only of the principles of thisinvention and are not intended to limit the scope of the invention tothe particular embodiments described. Thus, the invention is limitedonly by the following claims and their equivalents.

1. A metrology system comprising: a narrowband beam generation systemfor directing a narrowband probe beam at a measurement pattern on a testsample; a first sensor; a set of output optics for directinginelastically scattered light from the measurement pattern in responseto the narrowband probe beam onto the first sensor; a second sensor formeasuring elastically scattered light from the measurement pattern; anda computing system including: inelastic scatterometry logic forperforming an iterative operation to determine a material propertydistribution across the measurement pattern, the iterative operationusing the inelastically scattered data measured by the first sensor;logic for generating dimensional information for the measurement patternby performing a scatterometry analysis on elastically scattered lightdata for the measurement pattern measured by the second sensor; andlogic for generating a mathematical model using the dimensionalinformation.
 2. The metrology system of claim 1, wherein the narrowbandbeam generation system comprises: a laser for generating the narrowbandprobe beam; and focusing optics for directing the narrowband probe beamonto the measurement pattern.
 3. The metrology system of claim 1,further comprising an adjustment mechanism for changing an angle ofincidence between the narrowband probe beam and the test sample.
 4. Themetrology system of claim 1, further comprising an adjustment mechanismfor changing an azimuthal angle between the narrowband probe beam andthe measurement pattern.
 5. The metrology system of claim 1, wherein thenarrowband beam generation system comprises an adjustable beam generatorfor adjusting a wavelength of the narrowband probe beam.
 6. Themetrology system of claim 1, wherein the inelastic scatterometry logicincludes: control logic for generating a set of trial inelasticallyscattered light data by applying a trial distribution for a materialproperty of the measurement pattern to a mathematical model of themeasurement pattern; control logic for comparing the set of trialinelastically scattered light data to a set of measured inelasticallyscattered light data for the measurement pattern measured by the firstsensor; control logic for adjusting the trial distribution until the setof trial inelastically scattered light data matches the set of measuredinelastically scattered light data; and control logic for providing thetrial distribution as an output material property distribution when theset of trial inelastically scattered light data matches the set ofmeasured inelastically scattered light data to within a specifiedtolerance.
 7. The metrology system of claim 1, wherein the first sensorcomprises an array detector, and wherein the inelastically scatteredlight comprises coherent inelastically scattered light.
 8. The metrologysystem of claim 1, wherein the set of output optics comprises a blockingfilter for blocking elastically scattered light from the measurementpattern from reaching a spectrometer.
 9. The metrology system of claim1, wherein the first sensor comprises a spectrometer, and wherein theinelastically scattered light comprises incoherent inelasticallyscattered light.
 10. The metrology system of claim 8, wherein thenarrowband beam generation system comprises a polarizer for polarizingthe narrowband probe beam, and wherein the set of output optics furthercomprises an analyzer for measuring a polarization state of theinelastically scattered light.
 11. The metrology system of claim 9,further comprising: a beam splitter for directing the narrowband probebeam towards the measurement pattern and for directing elasticallyscattered light from the measurement pattern at the second sensor.
 12. Amethod for analyzing a semiconductor wafer, the method comprising:generating a first set of inelastically scattered light from ameasurement pattern on the semiconductor wafer; measuring a first set ofinelastic scattering data for the first set of inelastically scatteredlight; and determining a material property distribution across themeasurement pattern by analyzing the first set of inelastic scatteringdata while performing an iterative operation; generating a set ofelastically scattered light from the measurement pattern; measuring aset of elastic scattering data for the set of elastically scatteredlight; performing a scatterometry analysis on the set of elasticscattering data to determine a set of physical characteristics for themeasurement pattern; generating a mathematical model using the set ofphysical characteristics; and using the mathematical model during theiterative operation.
 13. The method of claim 12, wherein measuring thefirst set of inelastic scattering data comprises measuring coherentinelastically scattered light in the first set of inelasticallyscattered light using an array detector.
 14. The method of claim 12,wherein determining the material property distribution comprises:generating a set of trial inelastic scattering data by applying a trialdistribution for at least one material property in the measurementpattern to a mathematical model of the measurement pattern; comparingthe set of trial inelastic scattering data to the first set of inelasticscattering data; adjusting the trial distribution until the set of trialinelastic scattering data matches the first set of inelastic scatteringdata to within a specified tolerance; and providing the trialdistribution as the material property distribution for the measurementpattern when the set of trial inelastic scattering data matches thefirst set of inelastic scattering data to within the specifiedtolerance.
 15. The method of claim 12, wherein the measurement patternis dimensionally similar to functional devices on the semiconductorwafer, the method further comprising extracting a set of values for atleast one material property for the functional devices from the materialproperty distribution.
 16. The method of claim 12 wherein the materialproperty distribution further provides information regarding at leastone of stress, embedded charge, composition, and degree ofcrystallinity.
 17. The method of claim 12, further comprising:generating a second set of inelastically scattered light from themeasurement pattern; and measuring a second set of inelastic scatteringdata for the second set of inelastically scattered light, whereindetermining the material property distribution further comprisesanalyzing the second set of inelastic scattering data while performingthe iterative operation.
 18. The method of claim 12, wherein measuringthe first set of inelastic scattering data comprises measuringincoherent inelastically scattered light in the first set ofinelastically scattered light using a spectrometer.
 19. The method ofclaim 17, wherein generating the first set of inelastically scatteredlight comprises directing first narrowband probe beam at the measurementpattern, the first narrowband probe beam having a first polar anglerelative to the semiconductor wafer, a first azimuthal angle relative tothe first measurement pattern, and a first wavelength, whereingenerating the second set of inelastically scattered light comprisesdirecting a second narrowband probe beam at the measurement pattern, thesecond narrowband probe beam having a second polar angle betweenrelative to the semiconductor wafer, a second azimuthal angle relativeto the measurement pattern, and a second wavelength, and wherein atleast one of the second polar angle, the second azimuthal angle, and thesecond wavelength is different from the first polar angle, the firstazimuthal angle, and the first wavelength, respectively.
 20. The methodof claim 18, wherein the first set of inelastic scattering datacomprises a Raman spectrum.